The purpose of this study is to determine the safety and possible effectiveness of memantine,a drug which has been used for several years in Germany for the treatment of neurologicaldisorder (such as Parkinson's disease), but has not been approved in the U.S. for any disease state. This study will look to see if memantine is helpful in curbing some of the effects seen with AIDS Dementia Complex, or ADC. ADC causes damage to the nervous system, particularly the brain and spinal cord. People who have ADC may develop difficulty with calculations, difficulty understanding what they read or hear, slowing of thinking processes or difficulty in control of bladder or bowel function. The exact cause of ADC is unknown.